Denial to Issue Relieving Letter / Experience Letter

Hello Sir, This is in reference to issuance of relieving letter and experience letter by my last organisation. Kindly guide with the best suitable suggestions. Details are as follows:- I have worked with my previous Organisation for 5 years. I got a opportunity in another organisation and opted for the same, at my level notice period was of 90 days but I requested to relieve me after serving 1 month from my date of resignation and deduct the amount against my unserved notice period from my Full and Final Settlement. But my Function and HR Head was adamant on serving the full notice period. As new role was good and requirement was immediate, I decided to move on and documented on mail that I will be leaving after 39 days and will ensure to give proper handover to my team and colleagues as there was no plan to higher my replacement as organisation is going through merger. I have all mails available with me like sharing the status related to handover of my responsibilities, intimation on my last working day and details related to asset handover to IT and Commercial Teams. My F&F is processed within 20 days of my exit but HR team is not releasing experience letter and relieving letter. According to clause in my appointment letter any party can pay the dues against unserved notice period and terminate the contract. Kindly suggest the best possible way out to get the relieving letter and experience letter and also clarify is it possible that these 2 letters can be stopped by HR when there is nothing due against me. Regards,